Customarily, a slight clearance is provided between the surfaces of a sliding bearing and a rotating shaft which are disposed in sliding contact with each other when the rotating shaft is rotatably journalled by the sliding bearing. In such a conventional sliding bearing, when a smaller internal diameter of the surface of the sliding bearing which is disposed for sliding contact is chosen in an attempt to minimize the magnitude of the clearance, there results the disadvantage that a frictional resistance between the surfaces of the sliding bearing and the rotating shaft which are disposed in sliding contact with each other increases. Conversely, when a larger inner diameter is chosen for the sliding surface of the sliding bearing to increase the clearance and minimize the frictional resistance, there is another disadvantage that the occurrence of an impact sound between the surfaces increases. Thus, it has been difficult in a conventional sliding bearing to achieve a reduction in the frictional resistance between the sliding surfaces and a reduction in the impact sound simultaneously.